A magnetoresistive element, whose resistance changes with an applied magnetic field, has been developed actively for applications to devices such as a magnetic head and a magnetic random access memory (MRAM) that serves as a magnetic memory device. In particular, the magnetoresistive element including a tunnel junction has attracted considerable attention because of its potentially high MR ratio. Generally, the magnetoresistive element allows information to be written into a memory by changing the magnetization direction of a part of the ferromagnetic materials. The information is read from the memory by detecting a change in electrical resistance caused when the magnetization direction is changed.
The magnetoresistive element has been miniaturized steadily to meet the demand for mass storage or the like. It is expected that the miniaturization will increase a magnetic field required to change the magnetization direction of the ferromagnetic material. However, the magnetic field cannot be sufficiently high by increasing the current, since the conductor wires for generating the magnetic field should be miniaturized as well. Increasing the magnetic field causes crosstalk. The crosstalk causes malfunction of elements that are adjacent to the element to which the magnetic field should be applied. Under these circumstances, there is a limit to the mass storage and high integration of a device using a conventional magnetoresistive element.
Basic research on a material that can be controlled to be paramagnetic or ferromagnetic by application of a voltage has begun (H. Ohno; Nature, Vol. 408, 21/28 December (2000), p. 944). Such a material is called a magnetic semiconductor. The magnetic semiconductor is applied also to a magnetic head (JP 11(1999)-87796 A).